Improved furnace for desulphurizing ores



0. A.STETEFELDT. FURNACE FOR DESULF-URIZING ORES.

Patented June 14, 1864 w WM UNITED STATES PATENT OFFICE.

CHARLES A. STETEFELDT, OF NEW YORK, N. Y.

IMPROVED FURNACE FOR DESULPHURIZING ORES.

Specification forming part of Letters Patent No. 43.140, dated June 14,1864.

To all whom it may concern:

Be it known that I, CHARLES A. Srnrn- FELDT, of the city, county, andState of New York, have invented anew and Improved Figure 1 represents afront elevation of my invention. Fig. 2 is a transverse vertical sectionof the same, the line as m, Fig. 4., indicating the plane of section.Fig. 3 is a longitudinal vertical section of the same, taken in theplane indicated by the line Fig. 1. Fig.

4 is a plan or top View of the same. Fig. 5is

a side elevation of the same. Figs. 6, 7, and S are diagramsillustrating the shape and position of the terraces.

Similarletters of reference indicate the same parts in all the figures.

This invention relates to certain improvements in that class of furnacesknown as upright terrace-furnaces; and the object of these improvementsis to regulate the velocity with which the charge passes through thefurnace and to reduce the time necessary for a perfect roasting ordcsulphurization of the ores by the peculiar shape and construction ofthe terraces, and by their peculiar position in re lation to each other;also to reduce the expenditure of fuel and to regulate the temperaturethroughout the furnace by the application of hot-air apparatus andcold-air pipes in combination with the terra'ces,and to make suchdisposition in the internal arrangement that the furnace is applicablefor the reduction of gold, silver. quicksilver, and other ores.

The process of roasting is undoubtedly the most important of allmetallurgical operations, not only bccaus'e by means of it metals aredirectly produced from ores and furnace products-as, for instance, inthe manufacture of lead inreverberatories,the production of copper fromcopper matte, and the extraction of quicksilver from cinuabar-bnt thisprocess also forms the basis of all other metallurgical operations.

The necessary conditions for a quick and complete desulphurization ofores are as follows First. Minutedivision of the ores and presentationof the greatest possible surface.

Second. Introduction of the steady movement of the roasting-chargeagainst the current of combustion gases and air. Experience shows thatwhen the charge is left perfectly stationary, or'even when it is movedwith the current of air, the result is an incomplete desulphurization.

Third. Greatest possible usemade of the heat generated by the processitself aside from fueling. Fourth. A continuous and uniform modeofprocedure, which renders the success of theprocess more independent ofthe attention and skill of the workmen. I

My furnace is constructed with the View to fulfill theseconditions. Thepulverized ore is allowed to. fall I over a succession of terracesthrough an inclosed space or shaft, while a heated current of air orflame is conducted in the opposite direction. In the construction ofsuch a furnace the form and arrangement of the terraces is the essentialelement, as will be apparent from the following thorough and scientificinvestigation. The greatest or natural slope or talus 6f loose masses ismeasured by the an gle of friction, Q, inclosed by the plane of thetalus and a horizontal plane. This angle will naturally be smallerwhenthe pulverized ore, on arriving on the slope, possesses a certaininitial velocity than it is when the ore is heaped thereon by carefulracking from beneath. If, therefore, the angle of friction be determinedby the latter method, it may be surely assumed that the ore arriving onthe terraces with a certain initial velocity will slide off from thesame. At the same time care must be taken to make the angleQ, of thetalus as small as possible, to prevent the ore from passing tooquicklythrough the furnace. By various experiments with differentcrushed ores the angle of friction for careful piling was found to beabout thirty-five degrees. The slope of the terrace measured by theangle B A I), Fig. 6, therefore, is to be thirtyfive degrees, andconsequently the angle A B D inclosed by the two sloping sides ofterrace will be one hundred and ten degrees.

In order to determine the position of the several terraces in relationto each other, it is necessary to follow a single particle of the ore inits course through the furnace. The ore on leaving the feeder arrives onthe first terrace with a certain' velocity which depends upon thevertical distance between the point B of the terrace and the slide orfeeder F, Fig. .7. If this distance be designated by S, we have thevelocity C, with which the ore arrives at the terrace, expressed asfollows:

0:: 1/ 2gs ..1 I where 9 represents the acceleration of gravity. Onarriving upon the terrace the velocity of the ore is checked and it iscompelled to fall in an oblique direction along the inclined plane B A,and it moves toward the point A with a velocity il -:0 sin Q .;..2.

In falling over the inclined plane '13 A the ore acquires a velocitywhichis expressed by v 2gh, when h denotes the .vertical height B Q ofthe terrace, and if 'b. is equal to half the width of the terrace theheight h is equal to b tang Q, and :on arriving at the point A thevelocity of the ore is Those particles also which do notstrike theterrace exactly at its apex, but some at point M lower down, will leaveit at A with practically the same velocity, since'in that case in theequation for O, the value of the v first part, 0, will be greater, whilethe value of 'the second part, /2 gh, will be smaller, than in the firstcase. The falling body, subjected to the further influence ofgravitation,

and to the uniform-velocity O in thedirection B A, assumes a complexmotion and describes the parabola A P, Fig. 7.

I angled system of co-ordinates, A X and A Y, be drawn through the pointA, the point P.

If a rightcan be. determined where the ore will be found after-the lapseof a period, t,,' reckoned from the moment of leaving the terrace A.- v:The coordinates-of that point arey c t cos Q 4 gt gQ igi :'I 5 s F 2 c:cosz Q .i-i,

By meansof these two operations the relative positions of the terracesw'ill be determined.

' The time t which the orerhqnires to pass from A to P is expressed bythe following: e f- V 0% sin Q+2gx-c sin 'i) 6 And if t designates thetime which the ore requires to pass from the feeder to the terrace, andt, the time required by the ore in sliding over the slope of theterrace, "we havetZV- 7 hf m i c +2gb tang Q-c,);.- 8 By introducing thevalue of t into equation .4 we getco y=-, Veg sin Q,2-g x-c s1n Q). 9

If the vertical distance between the base of the first terrace and thatof the second be called H, and the horizontal distance between thenearest edges A, and I place the second ter- -race so that the orecoming from the first maystrike upon its apex B',, the ordinates of theterminus B of the parabolic path are-' x -:H,--h 10 y':A,+b 11 And byintroducing these values into the equations 5 and 9 we obtain thefollowing equations:

F ,I of sin Q+ 2g(H,-h)c, sin

Q)b 12 J .0 1 --g -:-br

These two equations afford all the essential elements for theconstruction'of the first pair of terraces, and it is only necessary todetermine the velocity O with which the ore begins its motion on thesecond terrace in order to find the relation of H and A for all further.

terraces. 1

The component velocities of the ore in the point P of the parabola are(see Fig. 8)

v,:c cos Q, Or, :setting for t its value from equation 6,

' 1=V i sinz Q+ 1 v separates itself into twocomponentsone-perpendicularto the plane A B and due in the direction PA. Calling the latter 1),, we have- I In the same. manner. we canseparate v, into a force, v,, in the direction TA B, and a forceperpendicular to A3, and we have- These equations remain the same ifwes'uppose P to be the point at which the ore falls upon the secondterrace and A B to be the slope of the terrace. We shall :then have l w."H."-

The ore leaves the second terrace with a velocity, O which is- G,=O,+\/2gh 15 I The formula 12,13, 14, and 15 may be con sidered general.If H be the vertical distance of the nth terrace from the (n-l-Dth, Atheir horizontal distances, O the initialvelocity of the ore upon thenth terrace, O the terminal velocity upon the same. we shall haveg jsinQ veg, sin" Q+2g(H h) j "0 co q 16 .l.- H,,z(A -}-2b)ian'g (m 1s theywill vary, since, in order to find H am] ,7

A the distance between the (n+1)th and the (n+2)th terraces we mustsubstitute in these equations for 0,, the 'differentvalue G It istherefore by no means indifferent whether we first assume a value for Hand find the corresponding values for A, or whether we derive, viceversa, the values of H 'from A. From a simple consideration it will beapparent that we must take A as constant, since by this quantity thehorizontal dimensions of the furnace will be regulated, and if A shouldbe made variable the practical execution of the furnace upon correctprinciples would be impossible. A being .eonstant, the values of H wouldbe different for each successive pair of terraces-a condition which canbe easily satisfied. From a further consideration of the equation 18 itwill be seen that it contains only one variable factorviz., the velocitywith which the ore leaves the terrace. H there fore consists of a sum oftwo members, of which the first, (A+2b,) tang Q, is the same is I "20%;cos' Q, variable. Of these two members the first or constant one is byfar the greatest, since in the second the value O which will always beconsiderabla appears squaredas a divisor.

In order to ascertain between what limits the valueof H may vary it isnecessary to consider the equation 16, which shows that for allterraces, while the second the velocity with which the ore begins tomove upon the nth terrace is not always positive, but, on the otherhand, can become zero or negative. This will be the case when Q V R Q-g( s-T 1v-1 Q Since the equation 16 is general we can substitute N forN-l and obtain for that value of C for which the initial velocity upon'the next terrace will be zero, the equation The solution of thisequation gives c iwlifi ..21

1/cosQ-sin"Q.

the ore will fall in such a manner as to tend .to run up instead of downthe slope of the terrace and to leap over the summit. The terraces beingdouble, however, this latter motion would be resisted by a similartendency of the particles coming from the opposite slope. This periodicpausein the downward motion of the ore is extraordinarily favorable forthe roasting process, since by it the ore is retained for a longerperiod in the furnace. The. minimum value of e is of course 0 \/2gh andthe maximum value of H therefore H (A+2b) tang Q. The minimum value of Hcannot be in general terms exactly stated, but it is evident that Hmustalways be somewhat smaller than (A-l'flb) tang Q. The height H dependsfurther upon the values assigned to the dimensions A and b. The questionfirst arises whether A shall be taken ,as positive, zero, or negative;Positive it cannot well be taken, since in that case the verticaldistances of theterraces or height H results too great, and

in consequence therefrom the furnace would ailord room for only a fewterraces. The distance A must therefore be zero or negative, and itslimits are o and -b. For the latter value H will be equal to b tangQ=h--that is,

.all the terraces will form a single inclined plane. From theseconsiderations it might seem advantageous to make the value of A asnearly as. possible -b, and by doing so the largest possible number ofterraces might be crowded into a comparatively small space,and therebythe ore delayed in its'fall; but in that case the resistance to thecurrent of air is increased to such an extent thatthe pressure of thedraft from the bellows will have to be increased in proportion, and inconsequence thereof the formation of dust, &c., is augmented, and theregularity in the operation of the furnace is disturbed. By making Azoall tithe formulae are simplified, and we obtain for H ::2b tangQ- andThe width of the terraces 2b must be fixed by practical experience. Iftaken -too large it would make H very great; but it must be large enoughto meet the requirements of durability, absorption of heat, andresistance of air.

The bearing and scope of the equations hereinbefore given will be fullyunderstood from the following example:.

Let b=OA ft., Q:35, s:0.4 ft., g- 32.2 ft., and we have H,,:0.5601 ft.-3.839O ft.

C And H ::0.5601ft.+0.2643ft.:=0.7644ft., Foro .-=c,,+ vg hT \Ve obtain-G =4.247O ft. +0 ..26

Since- 0:5.0754 ft. and O,:2.9l1.1 ft, \Ve have- 0,:42470 ft-{4.9111ft.- 7.15Sl ft, And it follo that 210 t.-!-0.074.9 ftz'otaso. Flirt 1 lO,:o.o.i52 f-,-4.8031 ft.#-: 1.1879 ft, From which- G z t. 2470 ft. andH. ,will be the maximum H. H,:0.764A f Further 0,:34950 ft.-2 .8 4=97ft. :'0.6453 ft. C ::4.2470 ft.+0.6453 ft.=4.8923 ft H,:O.5641ft.-!-0.0164 ft.:-0.5665 ft. Again- (3,252.9434 ft.-3.2S2S ft. 2 0.3394ft. G -4.2470 ft. H;=0.764 ft.

It is unnecessary to continue the calculation any further, since thevalues of H will be alternately 0.5663 feet and 0.7644 feet. Thevelocity of the ore will therefore become zero after passing twoterraces, and a periodical or intermittent motion will be the result,

which is of the greatest importance for the velocity of the current ofair in the sections of the furnace. This velocity ought to exceed fivefeet per second, and taking the following dimensions as a basis, we canfind the quantity of the charge: Let the length of the terrace be threefeet, h, 2b, 350., the same as above stated, and the charge consists ofiron pyrites,

v which are to be deprived of their entire contents of sulphur-viz., 53per cent. We assume that 25 per cent. of the oxygen does not. take partin the roasting, but escapes unchanged. The temperature in the furnaceshall not exceed 7 00 centigrade, (1,223 Fahrenheit.) Three English feetbeing 0.916 meters, there will pass through the section of one feeder inone second 340,840 cubic centimeters of air heated to 700 centigrade. Ata temperature of 0 centigrade, and the barom-- eter at0.76 meter, (30in'ch,) this air would take up a space of 95,594 cubic centimeters,weighing 123.6 grams; but of this quantity 21.01 grams of oxygen act inthe process and unite with 21.01 grams of sulphur to sulphurous acid,(50,.) This result corresponds to 39.65 grams of pyrites per second,which will give for twelve hours 1, 713,000-grams, or 34.26hundred-weight one hundred pounds 21) five hundred grams'to the pound.For a furnace with five feeders, the product of twelve hours will be onehundred and seventy-one hundredweight. Pulverizedores contain aboutonethird of their volume in empty interstices,

and since the specific gravity of. pyrites is 5,

the 39.65 grams of ore required per second willtake up a space of 11.9cubic centimeters, which the feed-rollers must supply; If the latter aresupplied with-semicircular flutes, it

' will be easy to calculate the number of revolutions required perminute.

Guided by the results obtained by this investigation I built my furnacein the following manner: I

K represents an upright shaft of rectangular section built up of brickand lined with fire-brick or any other suitable material. This shaftcontains the terraces L, which are diamend-shaped, as clearly shown inFig. 2 of the drawings, so that they can be turned if the upper side hasbeen injured, and thus will be more durable andabsorb and recommunicatemore heat, than they will if made with a triangular cross-section. Theymust be made of fire-clay and had better be covered with a coating ofgraphitic clay, which resists most perfectly the chemical action of the-roastingcharge. A square iron rod is placed in the center of eachterrace, so that the same can be built in the rear and front wall of thefurnace. The roof N of the furnace which is formed of fire-clay containsthe feed-openings F, and above these are situated the rollers E, bywhich the ore can be conveyed regularly and in the desired quantities tothe furnace. These rollers may be fluted in a direction parallel totheir axis. From the rollers the ore drops upon a roof-shaped surface,e,which checks its velocity. The sides of this roof are perpendicular tothe slope of the sides-of the feedopenings. On both sides of the shaft Kare the fire-places G, which serve for heating up the furnace, andincertain cases for keeping up a firejduring the process of roasting. The

fire-places and ash-holes are six-arranged that a draft can be createdfrom beneath through the pipes a. After the ore has passed down over theterraces L, it collects in the lower part of the shaft and can be.removed through an aperture, 6, and a subterranean passage, d.

When blende is roasted, it may be advisable to prolong the lower end ofthe furnace into a hearth. Above the arqh of the fire-place in each sideof the furnace a pipe, d, is set which conveys the heated air from thebellows. This pipe mayset lower down into the furnace below thefire-places on the sides of the pipes a, in which case the number ofterraces may be increased by putting an additional number below thelevelof the fire-bridge. Between this level and that of the arch of thefire-place no terraces should be put, since they would prevent theuniform distribution of the flame in the furnace.

YVhile building the front wall of the furnace, holes f should be leftopposite each terrace, so that the temperature in the shaft may beobserved and disturbances'may b'eremedied by means of proper tools.During the'roasting these openings must be closed.

Behind the shaft K is a chamber, K, Fig. 3, which contains a series ofoval pipes, 9. These pipes communicate with-the bellows, and throughthem the air for the bellows is heated. The shaft K communicates withthe chamber K by means of a fine, h, which is partially occupied by theuppermost terraces. On leaving the chamber K the gases pass into thechannel I, which leads to the chimney J, and above this channel the wetores from the stamps are spread to be thoroughly dried.

This furnace isapplicable to the desulphur ization of ores of everydescription, but particularly for treating auriferous sulphurets andmetals which are afterward to be treated by amalgamation. For materialsrich in sulphur no fire will be required after the furnace has once beenheated. It will then run itself, heating its own air, and requiring onlyto be kept charged. Zinc blende can be desulphurizedwvith Very littlefire. When it is desired to desulphurize ores and furnace products onlyto a certain degree, (which is the casein most smelting operations) theprocess can be perfectly regulated by the amount of ore conductedthrough the feeders, the quantity of air admitted, and the height givento the fur-- nace.

For many purposes, especially for roasting races is not new, and that aroasting-shaft is described by \Vhelpley and Storer in their patent ofJanuary 12, 1864.

What I claim as new, and desire to secure by Letters Patent, isi 1. Theemployment or use of an upright ter race-furnace, substantially such asherein de scribed, for the purpose of reducing gold, silver,quicksilver, and other metals from the sulphureted ores.

2. The peculiar construction, proportion,

and disposition of the terraces L in the shaft K, as based on the rulesdeduced from the formulze 1 to 24, whereby a complete and rapiddesulphurization of the ores is acc0n1- plished.

3. The combination of a hot-air apparatus with an uprightterrace-furnace, for the purpose substantially as set forth.

CHARLES A. STETEFELDT.

Witnesses:

W. HAUFF, I M. M. LIVINGSTON.

